The U.S. Environmental Protection Agency recently reinforced the current trend of natural gas-powered equipment when it granted certification to two of GE’s Waukesha engines for mobile, non-road applications: the L7044, a 1,680-horsepower, 1,200 kW 12-cylinder engine, and the smaller 5794, a 1,380 horsepower, 1,000 kW 12-cylinder engine.

Aaron Trexler, the senior product line manager at Waukesha Gas Engines, advocates replacing older diesels with this more flexible option for powering drill rigs and oilfield equipment, citing significant cost savings and lower emissions. The engines’ ability to run on cleaner natural gas and less expensive site gas doesn’t hamper its diesel-like performance, he says. Trexler was scheduled to take part in a panel discussion about natural gas technologies for drilling applications at last month’s HHP Summit in Chicago. National Driller caught up with him for a few questions about the advantages of running mobile rigs on rich-burn combustion.

Q: What is the significance of the mobile certification?

It drove our portfolio. It’s our ticket to play in the space. Certification is critical: either we have it or we don’t play. Under Title 40 CFR 1048 (the federal emissions code for non-road, spark-ignition engines), if it’s mobile—as engines cross state lines, non-road and over 19 kW, the EPA owns regulation, not the states. 

The key is that this is a uniform statute. We adhere to an aggressive schedule of testing and reporting. We tested at five load points to record emissions. By doing this, we pre-certify the engines. The customer doesn’t need to retest.

Q: How difficult was it to acquire?

As engine manufacturers, emissions for mobile units are regulated differently, so we had to understand that first. There are significant differences between rich-burn combustion and other natural gas engines. It was a challenge.

Q: What are some of the differences—and what are the benefits of the rich-burn engine?

Lean-burn engines offer efficiency, but there’s a trade-off. They don’t have the full flexibility; they run best at constant, low speed. A rich-burn engine has the flexibility to perform at speed, yet it still provides 80 percent fuel cost savings (verses diesel).

It’s certified with the EPA to run on propane, CNG (compressed natural gas) and LNG (liquefied natural gas)—just about anything as long as it’s gaseous. That’s an important benefit because it means you can take advantage of onsite fuel. The ability to use field gas saves money and reduces the environmental impact by as much as 95 percent. Some companies use LNG to drill the first two holes, then switch to onsite gas. With electronic controls in the engine, it’s possible to change fuels in half an hour.

Q: Unconventional gas is one of the most abundant sources of natural gas in the U.S. and supplies about a quarter of the gas we use, which cuts prices, reduces our dependence on foreign oil and adds jobs, but isn’t fracking controversial?

Fracking has been widespread the last five to six years. Recently, I’ve seen articles talking about the worry of diesel emissions surpassing the concern over water pollution. As Tier IV diesel regulations and ultra-low sulfur diesel mandates for non-road operations come on, there’s a tightness of supply that drives cost spikes. Natural gas is good technology.

Q: What is driving the trend toward natural gas more, economics or environmental issues?

Cost is a major factor, for sure. Producers always look for ways to save money. There are so many costs involved with diesel fuel: transporting, holding, extra tanks. … If you’re working on a site with multiple wells, gas is flowing already; there’s clean-burning gas onsite.

Using natural gas also reduces the environmental footprint up to 95 percent by reducing emissions such as NOx, CO and VOCs. PM (particulate matter) is a big issue with diesel engines, but it’s virtually unknown with natural gas engines.

Another benefit is CO2E equivalency—methane slip. There is no perfect burn, but a rich-burn engine achieves full combustion; it’s a 100 percent burn. There’s no methane escaping.

Q: Are there any downsides in performance?

Our engines are able to operate like diesel engines; they respond quickly and easily to the load.

Q: I’ve heard that maintenance costs are higher and the payback period can be long.

Maintenance costs are actually much less than with diesel. Natural gas is a dry fuel, so that provides advantages for maintenance. Service intervals are four to five times longer for oil changes and 25 to 35 percent longer for top-end overhauls.

The payback period depends on the market. Propane can be very cheap where it’s considered waste gas. In general, applications where field gas is used offer the most savings, but overall, payback can be reached in less than nine months.

Q: Are there certain applications better suited for rich-burn engines?

We’re still learning different segments of the market, but it’s currently being used in marine, rail and mining. It works well on multi-well pads and in enhanced oil recovery. We have a program working on displacing diesel to power a submersible pump for artificial lift.

The use of this engine in drilling proves the concept that natural gas works.

Q: Can this technology be retrofitted?

No, there are considerable differences. You can’t take a lean-burn engine and add a few parts to make it a rich-burn engine.

Q: So what does that mean for diesel engines now and in the future?

It renders them obsolete. There are plenty of uses for diesel engines in enhanced oil recovery, but due to spiking prices and limited availability of diesel fuel, we are looking at phasing out diesel engines. Natural gas is abundant; there’s a stable supply and price.